Unveiling the mechanism of N‐methylation of indole with dimethylcarbonate using either DABCO or DBU as catalyst
Abstract
Depending on the catalyst used, N‐methylation of indole with dimethylcarbonate (DMC) ‐ an environmentally friendly alkylation agent – yields different products. With 1,4‐diazabicyclo[2.2.2]octane (DABCO), the reaction forms only N‐methylated indole but with or 1,8‐diazabicyclo[5.4.0]undec‐7‐ene (DBU), both N‐methylated and N‐methoxycarbonylated indole are formed. Using direct ESI(+)‐MS monitoring to collect actual snapshots of the changing ionic composition of the reaction solution, we report on the interception and characterization of key intermediates for such reactions. Although a mechanism has been proposed with methoxycarbonylated base as the key intermediate for both DBU and DABCO, the ESI(+)‐MS data as well as B3LYP‐D3/6‐311+G** calculations suggest that the reaction of DMC with indole under either DABCO or DBU catalysis follow contrasting mechanisms.
Citation
Vendramini , P H , Zeoly , L A , Cormanich , R A , Buehl , M , Eberlin , M N & Ferreira , B R V 2021 , ' Unveiling the mechanism of N ‐methylation of indole with dimethylcarbonate using either DABCO or DBU as catalyst ' , Journal of Mass Spectrometry , vol. 56 , no. 3 , e4707 . https://doi.org/10.1002/jms.4707
Publication
Journal of Mass Spectrometry
Status
Peer reviewed
DOI
10.1002/jms.4707ISSN
1076-5174Type
Journal article
Description
B.R.V.F., P.H.V. and M.N.E. acknowledge the São Paulo State Science Foundation (FAPESP) and the Brazilian National Science Council (CNPq) for financial support. L.A.Z. thanks CNPQ for his PhD scholarship (142476/2018-8), R.A.C. thanks SDumont and CESUP. M.B. thanks the School of Chemistry and EaStCHEM for support and for access to a computer cluster maintained by Dr. H. Früchtl.Collections
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